Propylene ethylene copolymers may be used in the production of pipes.
For example, WIPO Pat. App. Pub. No. WO 97/33117, describes pipes comprising polypropylene plastic material having high creep resistance, high long-term pressure resistance, improved stiffness and resistance to rapid crack propagation. As described therein, catastrophic failure of a polypropylene plastic pipe is prevented when the pipe is made of several layers of different polypropylene plastic material, where at least one layer consists of a broad molecular weight distribution (MWD) polypropylene that provides the high creep resistance and at least one layer consists of an elastomer-modified polypropylene that improves the impact strength. The broad MWD polypropylene is a mixture of a very high molecular weight propylene random copolymer with 1-10 wt % of ethylene or higher alpha-olefin repeating units and a low molecular weight propylene polymer with a low (up to 1 wt %) or zero comonomer content.
When small diameter pipes are needed, it may be important to have limited pipe wall thickness, which allows for pipes containing less material and improved efficiency in terms of feed due to the higher internal diameter. However, when the wall thickness becomes smaller the pipe may become brittle, thus it is necessary to use a material having high impact resistance, especially at low temperature. Furthermore, the pipe material may require a high flexural modulus in order to obtain rigid pipes. In a polypropylene based composition, the Izod may be improved while the flexural modulus is lowered. As described herein, a small amount of heterophasic copolymers having certain features can be added to a propylene ethylene copolymer for improving impact/stiffness balance without compromising stiffness.